Merge branch 'jk/two-way-merge-corner-case-fix'

Fix a rather longstanding corner-case bug in twoway "reset to there" merge, which is most often seen in "git am --abort". * jk/two-way-merge-corner-case-fix: t1005: add test for "read-tree --reset -u A B" t1005: reindent unpack-trees: fix "read-tree -u --reset A B" with conflicted index